1. Field of the Invention
Embodiments of the invention relate to a substrate support.
2. Description of the Related Art
Thin film transistors have been made heretofore on large glass substrates or plates for use in monitors, flat panel displays, solar cells, personal digital assistants (PDA), cell phones, and the like. The transistors are made by sequential deposition of various films including amorphous silicon, both doped and undoped silicon oxides, silicon nitride, and the like in vacuum chambers. One method utilized for deposition of thin films is chemical vapor deposition (CVD).
CVD is a comparatively high temperature process requiring that substrates withstand temperatures on the order of 300 degrees Celsius to 400 degrees Celsius, with temperatures exceeding 500 degrees Celsius on developing. CVD film processing has found widespread use in the manufacture of integrated circuits on substrates. However, since the glass substrate is a dielectric material that is very brittle and is subject to sagging, warping or cracking when heated to high temperatures, care must be taken to avoid thermal stress and resulting damage during heating and cooling.
Systems exist currently to preheat substrates prior to processing and to conduct post-processing heat treatment operations. Conventional heating chambers have one or more heated shelves for heating an individual or a plurality of glass substrates. The glass substrate is typically supported above a shelf on spacers to improve heat uniformity and throughput. To minimize costs, conventional spacers are typically formed from easily machined metals, such as stainless steel, aluminum, aluminum nitride, and the like. However, conventional spacers may mar or otherwise damage the surface of the glass substrate, possibly resulting in imperfections in the glass surface. For example, annealing to produce low temperature polysilicon film requires heating the glass substrate to about 550 degrees Celsius, which can cause about 4 mm of thermal expansion in a 900 mm wide substrate. This thermal expansion results in the glass substrate sliding across the spacers on which the glass substrate is supported during heating and cooling. The resulting friction between the glass substrate and spacers has been shown to cause scratches, cracks, and other deformation defects in the glass substrates. For example, substrates may break along a scratch or other defect instead of along a desired location during cleaving processes that divide the substrate into multiple panels, rendering one or more panels defective.
Therefore, there is a need for a support that reduces substrate damage during processing.